Morrison's English mustard contained, per serving, the same amount of salt as a packet of crisps.

Professor Graham MacGregor from the Wolfson Institute of Preventive Medicine, and chairman of CASH, said: "Unnecessary amounts of salt are still being hidden in our food."

"This puts both adults and children at risk of developing high blood pressure which causes strokes, heart attacks and heart failure, the commonest cause of death and disability in the UK. It is the food industry's responsibility to take the salt out," he added.